It is most often advantageous in data processing devices to have an ability and a flexibility to change functional operating capabilities so as to enhance the versatility of the data processing devie in a variety of situations where different data solutions are required. Sucn function-changing of a data processng device may typically involve the use of a keyboard having a plurality of keys which may be assigned dual functions, or in a more complex environment three or more functions, with respective mode keys to denote which particular function applies to a given key at any one time instant.
For example, a simple four-function electronic calculator may have four individual operation mode keys respectively labelled as the four basis arithmetic functions--addition, subtraction, multiplication and division. In this instance, the number of keys required for a keyboard of a calaculator of this character is not excessive, thereby creating no problem in key-labelling. As the complexity of the data processing device increases, however, the matter of key-labelling begins to create a problem because of the added functions required by the device and the restrictions space and operability place upon the type of key-labelling to be used on the keyboard of such a device. Thus, by adding the trigonometric functions of sine, cosine, tangent and are cosine to the calculator, more keys having the appropriate labels applied thereto are required for the keyboard.
By continuing to add to the functional capability of the calculator, more and more keys are necessary for the keyboard, and a point is reached where keys must serve dual function roles and even beyond if all of the desired functions of the calculator are to be possible via keyboard entry. It will be appreciated that there is some higher limit as to the number of keys which may be added to a keyboard without causing a breakdown in operator performance. In the latter respect, as the number of keys included on a keyboard for a data processing apparatus increases beyond a certain point, operator performance begins to decline and then drops rapidly because of the confusion brought on by the clutter of keys, the difficulty in accomplishing the desired information processing, and intimidation because of keyboard complexity.
Thus, one of the limiting factors in the design of an operator interactive data processing apparatus, such as an electronic calculator, is the human factor in the ability of an operator in properly assessing and understanding the respective keys included in a data entry keyboard having a multiple number of function keys which input data to the processing unit of the apparatus in permitting the apparatus to perform a diverse number of processing applications. Perhaps the human factor limitation achieves its most distinctive character in association with a hand-held calculator, for example, because of the space resstrictions necessary for a keyboard of such a device.
Hand-held calculators have been constructed to perform a wide variety of computational tasks, such as business, basic mathematics, scientific, etc. with keyboards whose layout and number of keys are generally along the same lines with little change in size and complexity. One example of a calculator whose keyboard includes a number of keys at or approaching the upper limit of an operator to reasonably understand and use the keys in the manner for which they are designed in the operation of the calculator is disclosed in U.S. Pat. No. 4,208,720 Harrison. The calculator in U.S. Pat. No. 4,208,720 Harrison is a hand-held calculator with forty keys having seventy-nine labels associated therewith.
One approach toward minimizing the number of keys and labels therefor as required in a data processing apparatus has been the use of separate memory modules, each with its own set of key functions and its own particular computational tasks, with the basic data processing apparatus. In this approach, a plug-in memory module, which may take the form of a read-only-memory (ROM), a programmable read-only-memory (PROM), or a magnetic tape, for example, is electrically connected to the data processing unit of the apparatus by insertion into an appropriate electrical socket provided in the apparatus housing for that purpose. This memory module will supplement the basic operation functions of the data processing appartus with additional functions and supply any necessary new data to enable the data processing apparatus to perform the added functions. The substituion of memory modules in this manner in a data processing apparatus equipped to make use of such memory modules is primarily limited to the augmentation of the permanent functions built into the data processing apparatus, and is of less utility in enabling the data processing apparatus to perform computational tasks based upon significantly different functions attributable to keyboard entry.
Typically, an operator will enter data via a keyboard of the data processing apparatus. Individual keys, which are switches, may be permanently labelled to identify the functions associated therewith. As previously explained, the keys may be given a dual function, or beyond, by the use of appropriate mode keys, which when actuated from one status to another, will cause the functions of the individual keys to change also. Dual-function labelling of keys is commonly found on business-type and scientific-type hand-held calculators in present use. In some instances, the keyboard may include a set of blank or unlabelled keys adapted to be used with various cardboard or plastic overlays bearing appropriate key-function identifying labels. Prior to the present invention, efforts have been made to reduce the clutter of keys on keyboards of sophisticated data processing apparatuses, such as electronic hand-held calculators designed for advanced scientific use. Two such prior efforts are disclosed in U.S. Pat. Nos. 4,078,257 Bagley and 4,385,366 Housey, both of which are hereby incorporated by reference. Bagley and Housey each make use of transparent keys in which the transparency of each key is a visual display. In Bagley, a plurality of display planes each containing preselected symbols is provided. A mode selection key enables one of the display planes to be chosen for viewing through the transparent keys comprising the keyboard as a liquid crystal display, thereby labelling the respective keys of the keyboard with the symbols of the chosen display plane. Housey relies upon the use of a particular plug-in memory module to provide label identification for the plurality of keys via liquid crystal displays visible through each transparent key. The plug-in memory module may be replaced by a different plug-in memory module with a corresponding change in the function labels applicable to the keys. Thus, Bagley is limited to the symbols on specific display planes which may be selectively chosen to identify the functions of the individual keys of the keyboard, whereas Housey is limited to the symbols associated with a particular plug-in memory module as the function labels to be associated with the keys of the keyboard. In each instance, flexibility and versatility of key labelling is somewhat restricted.